In processes for producing semiconductors or optical materials, patterning techniques that form fine patterns (or micropatterns) using molds are now attracting much attention. As the patterning techniques, various methods are known, such as soft lithography, capillary force lithography, and imprint lithography. For example, the imprint lithography comprises transferring an uneven pattern formed on a mold to an imprinting resin (or a resin for imprint) by stamping to easily produce a resin structure having the uneven pattern.
For a process for producing a fine structure by nanoimprinting, a mold to be used includes a quartz glass mold, a nickel mold, and others. Generally, such a mold is hard to be released from a resin, and the mold is used after a mold release agent is applied to the surface of the mold. Meanwhile, a mold made of a silicone rubber has a high transparency and is easily detached from an imprinting resin, and the imprinting resin can be photo-cured with the mold stamped thereon. Thereafter, the cured imprinting resin can easily be released from the mold. In particular, since a curable silicone rubber having a polydimethylsiloxane (PDMS) unit is easy to harden and easy to obtain, a cured product (a silicone rubber) of the curable silicone rubber is being widely used as a material for forming a mold.
Unfortunately, the PDMS cured product has a low mechanical strength (such as Young's modulus or modulus of elasticity in tension), and a large-area mold made of the PDMS cured product is sometimes damaged (or broken) in releasing the imprinting resin from the mold. Thus, since a large-area mold made of the PDMS needs to have a sufficient thickness in order to ensure a mechanical strength necessary for handling, the production of the mold needs a large amount of the PDMS. A problem of the mold is a serious increase in the production cost. Accordingly, a thin mold having a high mechanical strength is needed.
Japanese Patent Application Laid-Open Publication No. 2007-1288 (JP-2007-1288A, Patent Document 1) discloses a soft mold comprising a support film and a mold surrounding the support film. The support film has a high UV transmittance and comprises two-way sheets, and the mold has an uneven pattern on a surface thereof. This document discloses a poly(ethylene terephthalate) (PET) film as the support film, and a mold composed of a PDMS cured product as the mold. According to this document, the soft mold as a thin film formed by surrounding the transparent film as a core material with the PDMS cured product has a reduced thickness while maintaining a mechanical strength thereof.
However, according to this document, due to a low adhesion strength between the support film and the PDMS cured product, repeated use causes separation of the support film from the PDMS cured product. Moreover, in a case where the support film has a large area, the support film less follows a curved surface. Further, the PET film as the support film is unfortunately easily deformable due to a low heat resistance.
Japanese Patent Application Laid-Open Publication No. 2007-146143 (JP-2007-146143A, Patent Document 2) discloses a transparent fiber-reinforced composite resin composition, as a resin composition used for a sealant, adhesive, or filler, comprising a cellulose fiber having an average fiber diameter of 4 to 200 nm and a liquid precursor of a matrix resin. This document discloses that the matrix resin preferably includes highly transparent acrylic resin, methacrylic resin, epoxy resin, and silicone resin. In Examples of this document, water in an aqueous suspension of a hydrated bacterial cellulose is replaced with a gel-formed silicone resin (TSE3051 manufactured by GE Toshiba Silicone) to prepare a fiber-reinforced composite resin composition having a fiber content of 10% and a cured product thereof.
However, this document does not disclose use of the fiber-reinforced composite resin composition as a mold having a fine uneven pattern or does not disclose details of the silicone resin. Moreover, the silicone resin used in Examples is a silicone compound having a low modulus of elasticity, what is called a silicone gel. The silicone gel is hard to handle and unsuitable as a material for a mold.